Sat, 28 Aug 2010
If you find that running Windows makes a GRUB 2-based system unbootable (Debian bug, Ubuntu bug), then I'd like to hear from you. This is a bug in which some proprietary Windows-based software overwrites particular sectors in the gap between the master boot record and the first partition, sometimes called the "embedding area". GRUB Legacy and GRUB 2 both normally use this part of the disk to store one of their key components: GRUB Legacy calls this component Stage 1.5, while GRUB 2 calls it the core image (comparison). However, Stage 1.5 is less useful than the core image (for example, the latter provides a rescue shell which can be used to recover from some problems), and is therefore rather smaller: somewhere around 10KB vs. 24KB for the common case of ext on plain block devices. It seems that the Windows-based software writes to a sector which is after the end of Stage 1.5, but before the end of the core image. This is why the problem appears to be new with GRUB 2.
At least some occurrences of this are with software which writes a signature to the embedding area which hangs around even after uninstallation (even with one of those tools that tracks everything the installation process did and reverses it, I gather), so that you cannot uninstall and reinstall the application to defeat a trial period. This seems like a fine example of an antifeature, especially given its destructive consequences for free software, and is in general a poor piece of engineering; what happens if multiple such programs want to use the same sector, I wonder? They clearly aren't doing much checking that the sector is unused, not that that's really possible anyway. While I do not normally think that GRUB should go to any great lengths to accommodate proprietary software, this is a case where we need to defend ourselves against the predatory practices of some companies making us look bad: a relatively small number of people do enough detective work to realise that it's the fault of a particular Windows application, but many more simply blame our operating system because it won't start any more.
I believe that it may be possible to assemble a collection of signatures of such software, and arrange to avoid the disk sectors they have stolen. Indeed, I have a first draft of the necessary code. This is not a particularly pleasant solution, but it seems to be the most practical way around the problem; I'm hoping that several of the programs at fault are using common "licence manager" code or something like that, so that we can address most of the problems with a relatively small number of signatures. In order to do this, I need to hear from as many people as possible who are affected by this problem.
If you suffer from this problem, then please do the following:
I hope that this will help me to assemble enough information to fix this bug at least for most people, and of course if you provide this information then I can make sure to fix your particular version of this problem. Thanks in advance!